Generally, a lens-barrel provided in a zooming camera includes a plurality of lenses, and at least two groups of lenses of the plurality of lenses are moved along an optical axis direction to change a focal length.
Japanese Patent Publication No. Sho 54-43373 discloses a lens lens-barrel in which a cam barrel formed in a surface thereof with a cam groove is held on a base plate rotatably around an optical axis, and rotation of the cam barrel causes a lens holding frame to slide along the cam groove in the cam barrel and move along an optical axis direction.
In the case of moving lenses on the side of a subject closer to the subject along the optical axis for ensuring a relatively long focal length in such a zoom lens lens-barrel, the cam barrel needs to be moved closer to the subject than the base plate along the optical axis. However, when the cam barrel is rotated around the optical axis and moved along the optical axis direction to move the lens frame along the optical axis, movement of the lens frame along the optical axis direction sometimes becomes unstable.
Japanese Patent Laid-Open Publication No. 2005-292212 discloses a lens-barrel in which a guide shaft (guide bar) is provided in a cam barrel parallel to an optical axis, and the guide shaft is fitted in a through hole formed parallel to the optical axis along an outer peripheral surface of a lens holding frame. The guide shaft is provided in the cam barrel, and thus the guide shaft functions as a guide rail of the lens holding frame, and increases stability of movement of the lens holding frame along an optical axis direction. However, in the zoom lens disclosed in Japanese Patent Laid-Open Publication No. 2005-292212, the guide shaft forms a barrier to prevent the cam barrel from being moved toward an image surface along the optical axis and retracted into a main body of a camera, making it difficult to reduce the length of the zoom lens lens-barrel in the optical axis direction.
Japanese Patent Laid-Open Publication No. Hei 6-294920 discloses a zoom lens including a fixed frame fixed to a main body of a camera, and a movable frame slidably held inside the fixed frame. The fixed frame is provided with an image surface side guide shaft that functions as a guide rail in movement of image surface side lenses along an optical axis, and the movable frame is provided with a subject side guide shaft that functions as a guide rail in movement of subject side lenses along the optical axis. Thus, two types of guide shafts are provided in a lens lens-barrel to allow the movable frame to be retracted into the main body of the camera without the guide shaft forming a barrier. However, in the zoom lens disclosed in Japanese Patent Laid-Open Publication No. Hei 6-294920, the subject side guide shaft is provided inside the movable frame, and the image surface side guide shaft is provided outside the movable frame, thereby increasing the diameter of the lens lens-barrel.